Another rare feature of collagen is its regular arrangement of amino acids. Its sequence generally follows the pattern Gly-X-Y, where X is proline, and Y is proline or hydroxyproline. There are very few other proteins with such regularity. The resulting structure is called a collagen helix.

Collagen occurs in many places throughout the body, and occurs in different forms known as types:

Type I collagen - This is the most abundant collagen of the human body. It is present in scar tissue[?], the end product when tissue heals by repair. It is also found in tendons.

Type II collagen - Articular cartilage

Type III collagen - This is the collagen of granulation tissue[?], and is produced quickly by young fibroblasts before the tougher type I collagen is synthesised.